Recently, the use of SSDs (Solid State Drives) which are storage media having higher performance than HDDs (Hard Disk Drives) is spreading. In general, SSDs are more expensive than HDDs, so that if it is necessary to construct and operate computer systems within a limited budget, the storage areas of the SSDs must be utilized efficiently, since it is not possible to allocate a large SSD capacity. One prior art technique for efficiently utilizing a small capacity of high-performance storage media is a hierarchical storage management (tiered storage management) technique that provides to a storage system a storage tier composed of an expensive and high-performance storage media and a low-performance and inexpensive storage media, wherein data having a high I/O (Input/Output) frequency is placed onto a high-performance storage media (high-level storage tier) and data having a low I/O frequency is placed onto an inexpensive storage media (low-level storage tier). Further, a data cache technique is provided, wherein data temporarily read from the storage system is copied to a storage area in the server (server cache), and subsequent accesses are performed using data stored in the server cache.
One method for further utilizing high-performance storage media efficiently is a method for controlling a cache memory in a computer system having cache memories both in a server and in a storage system, wherein the system is controlled so that data cached in the cache memory of the server will not be cached in the cache memory of the storage system, and data cached in the storage system will not be cached in the cache memory of the server (Patent Literature 1).